Compound action potentials recorded from the exposed eighth nerve in patients with intractable tinnitus.

Compound action potentials (CAP) were recorded directly from the exposed intracranial portion of the eighth nerve in 19 patients undergoing microvascular decompression (MVD) of the eighth nerve for intractable tinnitus. The waveform of the CAPs recorded in patients with tinnitus varied from normal to highly abnormal, but only in 1 patient were there distinct abnormalities in the waveform of the CAP that could not be attributed to the patient's hearing loss. The mean values of the latencies of the N1 and N2 peaks in the CAPs recorded from the exposed eighth nerve in patients with tinnitus and high-frequency hearing loss were virtually indistinguishable from the latencies obtained in patients with similar hearing loss but no tinnitus. There was no statistically significant difference between the latency of peak III in the brainstem auditory evoked potentials (BAEPs) in these two groups of patients, but the latency of peak V was slightly shorter (statistically significant) in the patients with tinnitus than it was in the patients without tinnitus.